1. Field of the Invention
This invention relates generally to the field of optical systems, and more particularly to safety interlocks for preventing accidental exposure to concentrated light beams conveyed by optical fibers.
2. Description of the Related Art
Optical fiber interconnections used for data communications or telecommunications applications usually operate in the near infrared. Typical wavelengths of these links, i.e. those used in most commercial fiber systems, are 830 nm, 1.3 .mu.m, and 1.55 .mu.m. These wavelengths are invisible to human vision, but may be focused by the human eye. This produces a potential hazard when a person looks into the end of an apparently dark fiber that is connected to an operating transmitter, or into the transmitter itself.
A transmitter for coupling a modulated light signal to a optical fiber transmission line produces a narrow cone of light at the exit of the transmitter or at the exit of the optical fiber. To mitigate the hazard, legal requirements exist to regulate the amount of external radiation when an optical fiber coupler is disconnected. These pose an obstacle to use of lasers with optical fiber channels. Existing systems have overcome this obstacle through the use of safety interlocks. These have taken the form of mechanical shutters that cover the end of unplugged fiber cables and other coupler-engagement sensing schemes which fail to address the danger of a broken or cut cable.
An electronic scheme which monitors for reflection from an open end has also been implemented, but involves pulsing the transmitter at a low duty cycle. While this keeps the radiation dosage below the retina-damage threshold, it adds significant complexity and cost to the transceiver.
As fiber optic systems become adapted to a greater number of everyday applications, fiber optic cables will become more accessible to the general public, and a consequent increase in danger of retinal damage will result. A need exists for an inexpensive fail-safe interlock that is not easily damaged or defeated, and which prevents accidental radiation exposure in the event of a broken or cut optical fiber cable without reducing the available data transmission bandwidth.